Three-phase AC motors are known from the prior art in various embodiments. What they all have in common is that, in said three-phase AC motors, coils are arranged in the stator, said coils being operated using phase-offset alternating currents such that an oscillating magnetic field is formed around each coil. The geometric arrangement of the coils and the associated phases are selected here in such a way that the magnetic fields of all the coils are superposed to form a rotating magnetic field that exerts a torque on the rotor.
A common design is in this case the three-phase AC motor having three phases, in which the coils are arranged on the stator in such a way that the magnetic fields generated by the coils are arranged at an angle of 120° with respect to one another and the associated phases are shifted by 120° with respect to one another. The individual oscillating fields are superposed here to form a rotating field, wherein the field amplitude remains constant and rotates at the frequency of the applied three-phase alternating current. Calculation methods that can be used to determine the resulting rotating field from a general geometric arrangement of coils and the associated phases are known to those skilled in the art from the literature (for example Rolf Fischer, “Elektrische Maschinen” [Electric Machines], Section 4.2).
In many cases, the primary voltage source provides a DC voltage, which first has to be converted to the necessary AC voltages by means of an inverter. Such a situation is present, in particular, in electric motors fed by a battery, as is the case in electric vehicles, for example. A common design of this conversion consists in that the desired AC voltage is generated by pulse-width modulation, wherein the shape of the voltage profile and the phase and frequency thereof can be set in a controlled manner in a broad range by controlling the modulator accordingly.
A further model is a three-phase AC motor having 6 phases. To this end, documents US Patent App. Pub. No. 2007120520, which is incorporated by reference herein, WO 2014132385, which is incorporated by reference herein, and WO 2014207858, which is incorporated by reference herein, disclose designs having two sets of three-phase windings and inverters for generating rotating fields. Document US 20090033251, which is incorporated by reference herein, discloses an electric motor, in which six phases are generated by means of an inverter in order to control the torque generated in the motor. Document US Patent App. Pub. No. 20160365821, which is incorporated by reference herein, addresses an electric motor having two sets of three-phase windings that can be operated in six phases.
These embodiments are designed to convert electrical energy to kinetic energy as efficiently as possible.